President Donald Trump waves as he walks to a dinner with European business leaders at the World Economic Forum, Thursday, Jan. 25, 2018, in Davos. (AP Photo/Evan Vucci)

The most contentious piece of President Donald Trump’s new proposal to protect the so-called Dreamers has nothing to do with them. It’s the plan’s potential impact on legal immigration that sparked fierce Democratic opposition Friday and appeared to sink chances for a bipartisan deal in Congress.

The proposal outlined Thursday by the White House would end much family-based immigration and the visa lottery program, moves that some experts estimate could cut legal immigration into the United States nearly in half.

The plan would protect some 700,000 young immigrants from deportation and provide a pathway to citizenship, an offer the White House described as a concession to Democrats. But it also represented a victory for immigration hawks and a seismic shift for immigration policy in the U.S., which has long centered on the question of how to stop illegal border crossings, not how to curb legal immigration.

“It’s an enormous change in rhetoric and position,” said Alex Nowrasteh of the conservative Cato Institute. “Forever, people have talked about illegal immigration and now this anti-legal immigration position is standard for much of the Republican Party.”

The Senate’s top Democrat, Chuck Schumer of New York, dismissed the plan Friday as a “wish list” for hard-liners. He acknowledged the bipartisan common ground on protections for the immigrants now shielded by the Deferred Action for Childhood Arrivals program, or DACA. But he accused Trump of using them as “a tool to tear apart our legal immigration system and adopt the wish list that anti-immigration hardliners have advocated for years.”

Democrats forced a government shutdown last weekend in attempt to expedite negotiations over the Dreamers, who are set to lose protection from deportation in March. Trump’s proposal was the first detailed public offer from the White House.

On Friday, the president accused Schumer of complicating the talks. “DACA has been made increasingly difficult by the fact that Cryin’ Chuck Schumer took such a beating over the shutdown that he is unable to act on immigration!” Trump wrote on Twitter.

By including curbs to legal immigration in his proposal, Trump elevated ideas that have been advocated by a slice of hardliners for decades, although with little momentum in Washington. Trump has framed the proposals as an attempt to prioritize immigrants with specific skills rather than family connections.

The U.S. takes in about 1 million legal immigrants annually, and nearly 13 percent of the country’s residents were born overseas, the highest share in nearly a century. Immigration hawks argue that the influx drives down native-born Americans’ wages and strains public resources.

“When you’re bringing in the equivalent of a major metropolitan area every year, that has an impact on every aspect of life,” said Ira Mehlman of the Federation for American Immigration Reform, which is the other major group advocating for fewer immigrants.

But many economists and businesses say there’s little data showing that immigration is bad for the economy, and much showing it is a net benefit. Though a few have found immigrants can depress some workers’ wages, most believe there’s little negative impact on on U.S. workers. In fact, because native-born U.S. citizens are having fewer and fewer children, some warn the U.S. faces a looming worker shortage and that immigrants are essential to keep the country growing.

A panel from the National Academy of Sciences in 2016 found that immigration had a small negative impact on some native-born workers who hadn’t graduated high school but also had many important benefits, such as fueling growth, innovation and entrepreneurship.

“At the end of the day. We’re either going to believe the data coming from businesses that are trying to grow the nation’s economy, or we can believe press statements,” said Ali Noorani of the National Immigration Forum, which supports increasing immigration. “Ultimately, this is not a question about economics. This is about the cultural anxiety coursing through the country that has been given an outlet by saying ‘immigrants are taking our jobs.'”

Trump tapped into that anxiety to win the election, pledging to build a wall along the southern border and make Mexico pay for it. He also vowed to end former President Barack Obama’s program to protect people brought to the U.S. as children and now living here illegally. But when he announced an end to DACA in September, he asked Congress to come up with a way to make the program permanent, arguing the young immigrants don’t deserve deportation.

Democrats offered to fund Trump’s border wall, then later retracted the offer. The administration then added to its list of demands, including changes to the family-based immigration system and an end to the lottery for visas for people from countries under-represented in the U.S. to its list of demands.

The plan would eliminate hundreds of thousands of family-related visas. Immigrants would only be allowed to sponsor their spouses and underage children to join them in the U.S., and not their parents, adult children or siblings.

But rather than shift those open slots to immigrants under a skills-based system, they would be applied to the backlog of immigrants waiting for a U.S. visa. Then, when that backlog is ended, the slots would be eliminated.

Nowrasteh of Cato estimates that the result could be a 40 percent to 45 percent reduction in overall immigration over time. The numbers depend on how the visas are applied to the backlogs — the immigration backlogs are so immense in some categories it could take decades to whittle them down. It’d take more than 130 years, he estimates, for all Mexicans waiting for a legal visa to get one.

Still, some immigration hawks were disappointed with the plan, arguing it could take decades before the reductions kick in. “The cuts in immigration don’t happen for 15 years,” complained Roy Beck of Numbers USA.